Computer-assisted, stereotactic systems, which operate with the aid of body structure data obtained from tomographic detection systems and with the assistance of x-ray images produced in situ, are known, for example, from U.S. Pat. Nos. 4,791,934 and 5,799,055. Supporting an operation using x-ray image recordings is discussed, for example, in U.S. Pat. Nos. 5,967,982, 5,772,594 and 5,784,431.
Even if accurate medical navigation is provided, the current prior art still operates with the aid of body structure data originating, for example, from tomographic detection systems, such as computer tomography devices or nuclear spin tomography devices. The patient to be treated is thus positionally registered in situ with respect to the previously ascertained image data. Operating instruments are then virtually displayed in the same relation to the image data as to the actual patient, in order to make the body structure data or possibly also x-ray image data useful to the surgeon in the operating theater.
One drawback of such methods, in which tomographic recordings (CT, MR) or x-ray images are produced especially for navigation within the context of a treatment, is the radiation load on the patient. Another drawback is the high cost, since such devices are very expensive both to purchase and to maintain and operate.
Attempts have been made to develop systems that may be used without body structure data captured separately in advance, for example, on the basis of statistical models of image data sets for body structure. However, such systems lack the required accuracy for the patient to be treated in each case.
DE 100 37 491 A1 and WO 99/59106 describe methods for providing 3-D information with the aid of fluoro-recordings. The starting point in all the methods is that of producing transillumination recordings of the patient, and/or the desired structure. A localization system is typically used for this, in order to obtain spatial information with the recordings. DE 100 37 491 A1 initially uses two fluoro-images, from which to reconstruct a rough 3-D model. Further recordings from different angles are used to specify the model even more exactly. In accordance with WO 99/59106, at least three fluoro-recordings of the patient are generally made. These can include anterior-posterior, lateral, and anterior-posterior with the head inclined back. In addition to the transillumination recordings, photographs of the patient are also used. In this prior art method, the model is elaborately adjusted in three-dimensional space.
A technique is known from WO 01/22368, using which a three-dimensional model is reconstructed using fluoroscopy images. The basis for this is a statistical model of the desired structure and at least one fluoroscopy image. The idea is to first position the model using the back-projected contours of the structure, such as are to be found in the fluoroscopy images. The model is then deformed and the contours of the deformed model are compared with the contours found in the fluoroscopy image. The quality of match is determined by calculating the error in the difference between the model contour and the fluoroscopy image contour. The two steps are repeatedly performed, i.e. the model is positioned and “morphed” until a good match is found.
One drawback of this method is that the degree of match between the model and the fluoroscopy image data is determined in the three-dimensional space, which includes the model. Such calculations are very complicated and time-consuming, which compromises its practical application. Furthermore, accuracy suffers from the fact that this method only uses a few features of the fluoroscopy images, namely only the contour lines.